In the microprocessing for manufacturing semiconductor devices or flat panel displays (FPD), it is of paramount importance to control a plasma density distribution, a temperature and the temperature distribution on the substrate to be processed (e.g., a semiconductor wafer and a glass substrate). If the temperature of the substrate is not properly controlled, it is difficult to secure process uniformity on the surface of the substrate, which leads to a reduced production yield of semiconductor devices and display devices.
In general, a mounting table or susceptor for mounting thereon a substrate to be processed inside a chamber of a plasma processing apparatus, particularly a capacitively coupled plasma processing apparatus, functions as a radio frequency electrode for applying a radio frequency power to a plasma space, as a support unit for supporting a substrate, e.g., by electrostatic attraction and as a temperature control unit for controlling the substrate at a predetermined temperature by heat conduction. The mounting table serving as the temperature control unit is required to properly compensate a heat distribution caused by a substrate supporting structure or a heat input characteristic distribution on the substrate caused by nonuniformity of a radiant heat from a plasma or a chamber wall.
Conventionally, in order to control a temperature of an upper surface of a susceptor (and eventually the temperature of a substrate), there has been frequently used a method for supplying a coolant whose temperature is controlled by a chiller unit into the coolant passageway provided inside a susceptor or a susceptor supporting table to be circulated therein. However, this chiller method encounters a difficulty in rapidly changing the coolant temperature and suffers from reduced responsiveness in temperature control. Thus, the chiller method has a shortcoming in that it is incapable of performing temperature change or raising and lowering of a temperature at a high speed. In an up-to-date process, e.g., in a plasma etching field, there is a need to successively process a multi-layered film of a substrate to be processed within a single chamber instead of multiple chambers used conventionally. The technique of raising and lowering the temperature of a mounting table at a high speed is essential in realizing the single-chamber processing. Under these circumstances, a heater method may be proposed for rapidly and accurately controlling a susceptor temperature and hence a substrate temperature by controlling Joule heat generated by a heating element which is installed in the susceptor to generate heat when energized (see, e.g., Japanese Patent Laid-open Application No. 2006-286733).
In case where a lower electrode high frequency application type in which a radio frequency power supply is connected to a susceptor for plasma control purposes is used in combination with the afore-mentioned heater method in which the heating element is provided in the susceptor for temperature control purposes, the operation or performance of a heater power supply may be impaired if a part of the radio frequency power applied from the radio frequency power supply to the susceptor flows into the heater power supply through the heating element and the heater power supply line as a noise. In particular, the heater power supply, which can be controlled at a high speed, is subjected to highly sensitive switching control or on/off control through the use of a semiconductor switching element such as a solid state relay (SSR) or the like. Therefore, the heater power supply is susceptible to erroneous operation if radio frequency noises flow into the same. In view of this, it is typical that the heater power supply line is provided with a filter circuit for sufficiently attenuating undesired radio frequency noises.
In general, this kind of filter circuit includes LC low-pass filters connected to one another in multistage like a ladder, each of which has a single coil (inductor) and a single capacitor. Assuming that a noise attenuation ratio per LC low-pass filter is equal to, e.g., 1/10, the radio frequency noise can be attenuated to 1/100 if the LC low-pass filters are connected in two stages and 1/1000 if the LC low-pass filters are connected in three stages.
As stated above, in the conventional plasma processing apparatus, the function of the filter circuit provided in the heater power supply line is focused on attenuation of the radio frequency noises, which flow from the radio frequency power supply to the heater power supply through the susceptor, in an effort to keep normal the operation or performance of the heater power supply. Thus, a low-inductance coil and a high-capacitance capacitor are used in the LC low-pass filters of each stage in the filter circuit.
During the process of developing and evaluating a plasma processing apparatus in which a lower electrode high frequency application type and a heater are used in combination in a susceptor, the present inventors have found that the afore-mentioned conventional filter circuit has a problem in terms of process performance. More specifically, it is well-known that there exists a correlation between the power loss of a radio frequency power applied from a radio frequency power supply to a susceptor and the process performance (e.g., an etching rate), according to which the process performance is reduced as the radio frequency power loss becomes greater. The present inventors were able to learn that a significant amount of radio frequency power loss not negligible in terms of the process performance occurs in the conventional filter circuit. Furthermore, the present inventors were able to find that there is a variance (apparatus-dependent difference) in the amount of radio frequency power loss between plasma processing apparatuses even if they are of the same nature, which leads to an apparatus-dependent difference in the process performance. Under this critical mind, the present inventors have repeatedly conducted experiments and researches and have succeeded in finalizing the present invention.